Pseudomonas aeruginosa produces pyoverdine, encoded by the pvdE gene, for high-affinity iron uptake from transferrin and lactoferrin. This study investigated the contribution of pyoverdine to P. aeruginosa keratitis pathogenesis using in vitro and in vivo models.
The P. aeruginosa strains examined were parental strain PAO1 and isogenic mutant strain pvdE (ΔpvdE) defective in pyoverdine. Bacterial growth in vitro was determined by PAO1 and ΔpvdE optical densities in Luria–Bertani (LB) broth. PAO1 or ΔpvdE (108 colony-forming units/mL) was inoculated onto cultured human corneal epithelial cells (HCECs) for 1 hour. The monolayers were examined for bacterial adhesion and invasion. In addition, the corneas of C57BL/6 mice were infected with PAO1 or ΔpvdE. Corneal virulence was evaluated by determining clinical scores and bacterial counts during infection.
The growth of PAO1 and ΔpvdE in LB broth was similar. Although adhesion of ΔpvdE onto HCECs was significantly increased compared with PAO1, the invasive capacity of ΔpvdE was significantly decreased. Clinical scores and bacterial numbers were significantly lower in ΔpvdE-infected eyes compared with PAO1-infected eyes at 6, 24, and 48 hours (P < 0.001). ΔpvdE was not detected in mouse corneas and did not induce corneal opacity at 6, 24, or 48 hours.
ΔpvdE lost invasive ability toward HCECs. Moreover, ΔpvdE did not cause keratitis in vivo. Thus, pvdE pyoverdine synthesis has critical roles in proliferation and invasion on ocular surfaces and could be a target for prevention of P. aeruginosa keratitis.
*Ishizuchi Eye Clinic, Ehime, Japan;
†Department of Ophthalmology, Ehime University School of Medicine, Ehime, Japan; and
‡Department of Microbiology and Infection Control Sciences, Kyoto Pharmaceutical University, Kyoto, Japan.
Correspondence: Takashi Suzuki, MD, PhD, Ishizuchi Eye Clinic, Niihama, Ehime 792-0811, Japan (e-mail: firstname.lastname@example.org).
Supported by the Department of Bioscience, INCS, Ehime University.
The authors have no funding or conflicts of interest to disclose.
Received June 28, 2018
Accepted July 03, 2018